FEATURES
s
s
s
s
s
LTC3700
Constant Frequency
Step-Down DC/DC Controller
with LDO Regulator
DESCRIPTIO
The LTC
®
3700 is a constant frequency current mode step-
down (buck) DC/DC controller with excellent AC and DC
load and line regulation. The on-chip 150mA low dropout
(LDO) linear regulator can be powered from the buck
controller’s input supply, its own independent input supply
or the buck regulator’s output. The buck controller incor-
porates an undervoltage lockout feature that shuts down the
controller when the input voltage falls below 2.1V.
The buck regulator provides a
±2.5%
output voltage accu-
racy. It consumes only 210µA of quiescent current in nor-
mal operation with the LDO consuming an additional 50µA.
In shutdown, a mere 10µA (combined) is consumed.
For applications where efficiency is a prime consideration,
the buck controller is configured for Burst Mode operation
which enhances efficiency at low output current. To fur-
ther maximize the life of a battery source, the external
P-channel MOSFET is turned on continuously in dropout
(100% duty cycle). High constant operating frequency of
550kHz allows the use of a small external inductor.
The LDO is protected by both current limit and thermal
shutdown circuits.
The LTC3700 is available in a tiny 10-pin MSOP.
s
s
s
s
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Dual Output Regulator in Tiny 10-Pin MSOP
High Efficiency: Up to 94%
Wide V
IN
Range: 2.65V to 9.8V
Constant Frequency 550kHz Operation
150mA LDO Regulator with Current Limit and
Thermal Shutdown Protection
High Output Currents Easily Achieved
Burst Mode
®
Operation at Light Load
Low Dropout: 100% Duty Cycle
Current Mode Operation for Excellent Line and Load
Transient Response
0.8V Reference Allows Low Output Voltages
Low Quiescent Current: 260µA Total
Shutdown Mode Draws Only 10µA Supply Current
Common Power Good Output for Both Supplies
APPLICATIO S
s
s
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Notebook Computers
Portable Instruments
One or Two Li-Ion Battery-Powered Applications
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
V
IN1
5V
C1
10µF
10V
R1
0.068Ω
V
IN
SENSE
–
PGATE
V
IN2
LDO
169k
V
FB2
78.7k
C3
10µF
10V
V
IN2
3.3V
90
V
OUT2
2.5V AT
150mA
86
82
78
EFFICIENCY (%)
V
OUT1
1.8V
AT 1A
C2
47µF
6V
L1
10µH
100k
M1
C4
2.2µF
16V
D1
LTC3700
+
80.6k
V
FB
10k
I
TH
/RUN
220pF
GND
PGOOD
C1, C3: TAIYO YUDEN EMK325BJ106MNT
C2: SANYO POSCAP 6TPA47M
C4: MURATA GRM42-6X7R225K016AL
D1: MOTOROLA MBRM120T3
L1: COILTRONICS UP1B-100
M1: Si3443DV
3700 F01
R1: DALE 0.25W
Figure 1. High Efficiency 5V to 1.8V/1A Buck with 3.3V to 2.5V/150mA LDO
U
U
U
Buck Efficiency vs Load Current
V
OUT
= 1.8V
R
SENSE
= 0.068Ω
V
IN
= 3.3V
74
70
66
62
58
54
50
1
V
IN
= 4.2V
V
IN
= 5V
10
100
LOAD CURRENT (mA)
1000
3700 F01a
3700f
1
LTC3700
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
V
IN2
LDO
V
FB2
PGOOD
GND
1
2
3
4
5
10
9
8
7
6
I
TH
/RUN
V
FB
SENSE
–
V
IN
PGATE
Buck Input Supply Voltage (V
IN
) ................– 0.3V to 10V
SENSE
–
, PGATE Voltages ............. – 0.3V to (V
IN
+ 0.3V)
V
FB
, I
TH
/RUN Voltages ..............................– 0.3V to 2.4V
PGATE Peak Output Current (< 10µs) ....................... 1A
LDO Input Supply Voltage (V
IN2
) .................– 0.3V to 6V
LDO, V
FB2
Voltages ..................... – 0.3V to (V
IN2
+ 0.3V)
PGOOD Voltage .........................................– 0.3V to 10V
LDO Peak Output Current (< 10µs) ..................... 500mA
Storage Ambient Temperature Range ... – 65°C to 150°C
Operating Temperature Range (Note 2) ... –40°C to 85°C
Junction Temperature (Note 3) ............................. 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
LTC3700EMS
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 150°C,
θ
JA
= 230°C/ W
MS PART MARKING
LTXN
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= V
IN2
= 4.2V unless otherwise specified. (Note 2)
PARAMETER
Buck DC/DC Controller
Input DC Supply Current
Normal Operation
Sleep Mode
Shutdown
UVLO
Undervoltage Lockout Threshold
Shutdown Threshold (at I
TH
/RUN)
Start-Up Current Source
Regulated Feedback Voltage
Output Voltage Line Regulation
Output Voltage Load Regulation
V
FB
Input Current
Overvoltage Protect Threshold
Overvoltage Protect Hysteresis
Oscillator Frequency
Gate Drive Rise Time
Gate Drive Fall Time
Peak Current Sense Voltage
Peak Current Sense Voltage in Burst Mode
V
FB
= 0.8V
V
FB
= 0V
C
LOAD
= 3000pF
C
LOAD
= 3000pF
(Note 6)
500
V
ITH
/RUN = 0V
(Note 5), 0°C to 70°C
(Note 5), –40°C to 85°C
2.65V
≤
V
IN
≤
9.8V (Note 5)
I
TH
/RUN Sinking 5µA (Note 5)
I
TH
/RUN Sourcing 5µA (Note 5)
(Note 5)
Measured at V
FB
0.820
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
Typicals at V
IN
= 4.2V (Note 4)
2.65V
≤
V
IN
≤
9.8V
2.65V
≤
V
IN
≤
9.8V
2.65V
≤
V
IN
≤
9.8V, V
ITH
/RUN = 0V
V
IN
< UVLO Threshold
V
IN
Falling
V
IN
Rising
q
q
q
MIN
TYP
MAX
UNITS
210
200
10
10
1.90
2.00
0.15
0.25
0.780
0.770
2.10
2.20
0.30
0.5
0.800
0.800
0.1
4
4
10
0.860
20
550
110
40
40
120
30
340
330
30
30
2.60
2.65
0.45
0.85
0.820
0.830
mV/V
mV/µA
mV/µA
50
0.910
650
nA
V
mV
kHz
kHz
ns
ns
mV
mV
2
U
W
U
U
W W
W
µA
µA
µA
µA
V
V
V
µA
V
V
3700f
LTC3700
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= V
IN2
= 4.2V unless otherwise specified. (Note 2)
PARAMETER
LDO Regulator
V
IN2
Input Voltage
Input DC Supply Current
Normal Operation with Buck Enabled
Normal Operation with Buck Undervoltage
Shutdown with Buck Enabled
Shutdown with Buck Undervoltage
Regulated Feedback Voltage
Output Voltage Line Regulation
With Buck Enabled
With Buck Enabled
With Buck Undervoltage
Output Voltage Load Regulation
V
FB2
Input Current
LDO Short-Circuit Current
LDO Dropout
Overtemperature Trip Point
Overtemperature Hysteresis
PGOOD
Feedback Voltage PGOOD Threshold
PGOOD High-to-Low
PGOOD Low-to-High
PGOOD On-Resistance
(Note 8)
V
FB
or V
FB2
Falling
V
FB
or V
FB2
Rising
V
FB
or V
FB2
Rising
V
FB
or V
FB2
Falling
V
ITH/RUN
= 0V, V
IN
= V
IN2
= 4.2V, V
PGOOD
= 100mV
– 12
– 10
– 7.5
7.5
– 5.0
5.0
135
%
%
%
%
Ω
V
LDO
= 0V
V
IN2
= 3.3V, I
LDO
= 150mA
V
IN2
= 6V, I
LDO
= 150mA
(Note 7)
(Note 7)
150
Typicals at V
IN2
= 4.2V
2.4V
≤
V
IN2
≤
6V
2.4V
≤
V
IN2
≤
6V
2.4V
≤
V
IN2
≤
6V, V
ITH/RUN
= 0V
2.4V
≤
V
IN2
≤
6V, V
ITH/RUN
= 0V
0°C
≤
T
A
≤
70°C, I
LDO
= 1mA
–40°C
≤
T
A
≤
85°C, I
LDO
= 1mA
(Unity-Gain Feedback)
2.65V
≤
V
IN
≤
9.8V
2.4V
≤
V
IN2
≤
6V, I
LDO
= 1mA
2.4V
≤
V
IN2
≤
6V, I
LDO
= 1mA
1mA
≤
I
LOAD
≤
150mA
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
2.4
TYP
MAX
6
UNITS
V
µA
µA
µA
µA
V
V
mV/V
mV/V
mV/V
50
100
0
8
0.780
0.765
0.800
0.800
0.05
4
4
0.06
0
200
270
170
150
5
100
150
1
24
0.830
0.835
0.12
10
mV/mA
nA
mA
mV
mV
°C
°C
12
10
180
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3700 is guaranteed to meet specifications from 0°C to
70°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
•
θ
JA
°C/W)
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5:
The LTC3700 is tested in a feedback loop that servos V
FB
to the
output of the error amplifier.
Note 6:
Peak current sense voltage is reduced dependent on duty cycle to
a percentage of value as given in Figure 2.
Note 7:
Guaranteed by design; not tested in production.
Note 8:
PGOOD values are expressed as a percentage difference from the
respective “Regulated Feedback Voltage” as given in the table.
3700f
3
LTC3700
TYPICAL PERFOR A CE CHARACTERISTICS
BUCK DC/DC CONTROLLER
V
FB
Voltage vs Temperature
805
NORMALIZED FREQUENCY SHIFT (%)
804
803
V
FB
VOLTAGE (mV)
802
801
800
799
798
797
796
795
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3700 G01
V
IN
= 4.2V
I
TH
/RUN = V
FB
NO LOAD
Shutdown Threshold vs
Temperature
400
380
360
I
TH
/RUN VOLTAGE (mV)
V
IN
= 4.2V
2.30
2.28
2.26
TRIP VOLTAGE (V)
340
320
300
280
260
240
220
200
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3700 G04
Buck Supply Current
vs Input Voltage
250
240
V
IN
SUPPLY CURRENT (µA)
230
220
210
200
190
180
170
160
150
2
I
TH
/RUN = V
FB
V
IN2
= 0V
T
A
= 25°C
TRIP VOLTAGE (mV)
3
8
6
5
4
7
V
IN
INPUT VOLTAGE (V)
4
U W
Normalized Oscillator Frequency
vs Temperature
10
8
6
4
2
0
–2
–4
–6
–8
–10
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3700 G02
V
IN
= 4.2V
Undervoltage Lockout Trip
Voltage vs Temperature
2.24
2.20
2.00
2.18
2.16
2.14
2.12
V
IN
RISING
V
IN
FALLING
2.10
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3700 G03
Maximum (V
IN
– SENSE
–
) Voltage
vs Duty Cycle
130
120
110
100
90
80
70
60
V
IN
= 4.2V
T
A
= 25°C
9
10
50
20
30
40
50 60 70 80
DUTY CYCLE (%)
90
100
3700 G10
3700 G05
3700f
LTC3700
TYPICAL PERFOR A CE CHARACTERISTICS
LDO REGULATOR
V
FB2
Voltage vs Temperature
850
840
830
V
FB2
VOLTAGE (mV)
V
FB2
VOLTAGE (mV)
820
810
800
790
780
770
760
750
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3700 G06
V
IN2
= 4.2V
LDO = V
FB2
I
LOAD
= 1mA
I
LOAD
= 10µA
LDO Pass FET R
ON
vs Input
Voltage
4.0
3.7
3.4
3.1
V
IN
= 0
ILDO = 100mA
T
A
= 25°C
PGOOD R
ON
(Ω)
R
ON
(Ω)
2.8
2.5
2.2
1.9
1.6
1.3
1.0
2
2.5
3 3.5 4 4.5 5
V
IN2
INPUT VOLTAGE (V)
5.5
6
LDO Supply Current
vs Input Voltage
LDO = V
FB2
110 I
LDO
= 10µA
T = 25°C
100
A
90
80
70
60
50
40
30
20
2
2.5
3.5 4
3
4.5 5
V
IN2
INPUT VOLTAGE (V)
5.5
6
V
IN
= 9.8V
120
V
IN
= 0V
V
IN2
SUPPLY CURRENT (µA)
U W
LDO Line Regulation (V
FB2
Voltage vs Supply)
850
840
830
820
810
800
790
780
770
760
750
2.4 2.85 3.3 3.75 4.2 4.65 5.1 5.55
V
IN2
INPUT VOLTAGE (V)
6
I
LOAD
= 10mA
I
LOAD
= 100mA
I
LOAD
= 10µA
I
LOAD
= 1mA
T
A
= 25°C
LDO = V
FB2
I
LOAD
= 10mA
I
LOAD
= 100mA
3700 G07
PGOOD R
ON
vs Input Voltage
300
270
240
210
180
150
120
90
60
30
0
2
3
4
5
6
7
8
V
IN
INPUT VOLTAGE (V)
9
10
V
IN2
= 0V
V
PGOOD
= 100mV
T
A
= 25°C
3700 G08
3700 G09
Load Transient Response
150
I
LDO
(mA) 100
50mA/DIV 50
0
∆V
LDO
20mV/DIV
AC COUPLED
0
T
A
= 25°C
V
IN2
= 3.3V
V
LDO
= 2.5V
C
LDO
= 10µF
20µs/DIV
3700 G12
3700 G11
3700f
5
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